Recently, the techniques concerning the construction and operation of endoscopes are quickly advancing, and now the endoscope is not a mere tool for observing the inside of the body but is also used as means for the treatment and extraction of poleave. As a consequence, the number of requisite items accommodated in the tube such as the pincette guide, water duct and air duct and also the diameter of the tube are increasing. Increasing the diameter of the tube, however, means increased pain for the patient; particularly, with a tube greater in diameter than the size of the gullet, various inconveniences are encountered due to pressure exerted to the windpipe.
As another aspect, for varying the orientation of the endoscope inserted inside the body, which will be required for varying the direction of transmitted light flux and image light flux through the light transmitting fiber bundle or varying the direction of flow of water, the tube tip is rotated by rotating the grip. Accordingly, the tube desirably has a circular sectional profile. However, the sectional profile of the gullet is normally rather flat, and which is not conformed to by the tube.